AvrA Exerts Inhibition of NF-κB Pathway in Its Naïve Salmonella Serotype through Suppression of p-JNK and Beclin-1 Molecules

Avian salmonellosis caused by Salmonella enterica serovar Enteritidis (S. Enteritidis) and Pullorum (S. Pullorum) remains a big threat to the poultry industry and public hygiene. AvrA is an effector involved in inhibiting inflammation. Compared to AvrA from S. Enteritidis (SE-AvrA), the AvrA from S. Pullorum (SP-AvrA) lacks ten amino acids at the C-terminal. In this study, we compared the anti-inflammatory response induced by SP-AvrA to that of SE-AvrA. Transient expression of SP-AvrA in epithelial cells resulted in significantly weaker inhibition of NF-κB pathway activation when treated with TNF-α compared to the inhibition by SE-AvrA. SP-AvrA expression in the S. Enteritidis resulted in weaker suppression of NF-κB pathway in infected HeLa cells compared to SE-AvrA expression in the cells, while SP-AvrA expressed in S. Pullorum C79-13 suppressed NF-κB activation in infected HeLa and Caco 2 BBE cells to a greater extent than did SE-AvrA because of the higher expression of SP-AvrA than SE-AvrA in S. Pullorum. Further analysis demonstrated that the inhibition of NF-κB pathway in Salmonella-infected cells corresponded to the downregulation of the p-JNK and Beclin-1 protein molecules. Our study reveals that AvrA modifies the anti-inflammatory response in a manner dependent on the Salmonella serotype through inhibition of NF-κB pathway.